TW201316598A - Positive electrode material for lithium ion secondary battery, positive eletrode member for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Abstract

The present invention provides a positive electrode material for lithium ion secondary battery, a positive electrode member for lithium ion secondary battery and a lithium ion secondary battery. The positive electrode material for lithium ion secondary battery is a positive electrode material for lithium ion secondary battery comprising an oxide represented by empirical formula Li2+x(M, MA)(Si, MB)O4 and is characterized by 0 < x ≤ 0.25 in the empirical formula of the oxide (wherein M is at least one of elements selected from the group consisting of Fe, Mn, Co and Ni; and MA and MB respectively replace one part of M and Si and they are elements for charge compensation of x part of Li+.)

Description

Positive electrode material for lithium ion secondary battery, positive electrode member for lithium ion secondary battery, and lithium ion secondary battery

The present invention relates to a positive electrode material for a lithium ion secondary battery, a positive electrode member for a lithium ion secondary battery, and a lithium ion secondary battery.

Compared with conventional lead secondary batteries or nickel-cadmium secondary batteries, lithium ion secondary batteries have been widely used as mobile phones or notebook personal computers because of their light weight and large capacity. The power supply of the instrument. Recently, it has also been used as a battery for electric vehicles, plug-in hybrid vehicles, electric two-wheelers, and the like.

Basically, a lithium ion secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator.

Usually, the negative electrode is made of metallic lithium, carbon which can be inserted and desorbed from lithium ions, or lithium titanate. The electrolyte uses a lithium salt and an organic solvent or an ionic liquid (ionic liquid) capable of dissolving the same. The separator is provided between the positive electrode and the negative electrode and ensures insulation therebetween, and a porous organic resin or glass fiber having a pore that can pass through the electrolyte is used.

Basically, the positive electrode is composed of an active material capable of deintercalating lithium ions, a conductive auxiliary agent for ensuring a conductive path (electron conduction path) of the current collector, and a binding agent for combining the active material and the conductive auxiliary agent. . As the conductive auxiliary agent, a carbon material such as acetylene black, carbon black, or graphite can be used. Further, as the active material of the positive electrode material, lithium such as LiCoO ₂ , LiNiO ₂ , LiNi _0.8 Co _0.2 O ₂ or LiMn ₂ O ₄ and a metal oxide of a transition metal can be generally used. In addition, there are also derivatives in which LiMPO ₄ and the lithium metal phosphate are used as basic structures to change their elemental substitution or composition, and Li ₂ MSiO ₄ or the lithium metal silicate metal salt is used as a basic structure to change its element substitution or composition. A derivative in which LiMBO ₃ or the lithium metal borate metal salt is used as a basic structure to change its element substitution or composition. Among them, M mainly contains a transition metal element having a valence of Fe, Mn, Ni, Co or the like.

In general, since the metal oxide has a low electron conductivity, the positive electrode using a metal oxide as an active material is mixed with the above-mentioned conductive auxiliary agent. In addition, by mixing the conductive auxiliary agent, carbon is coated on the surface of the metal oxide active material, or carbon particles or carbon fibers are adhered to the surface, and the electron conductivity in the positive electrode is further improved (see Patent Documents 1 to 6). Non-patent document 1).

In particular, in the case of a metal oxide in which electron conductivity is remarkably lacking, it is insufficient to form a positive electrode by merely coexisting a conductive auxiliary agent, and since excellent battery characteristics cannot be obtained, the surface of the metal oxide is coated with carbon. used.

Further, among the above oxides, Li ₂ MSiO ₄ typified by lithium iron ruthenate or lithium manganese ruthenate or a metal salt of the lithium niobate as a basic structure, a derivative in which the element is substituted or the composition is changed, Since the two empirical formulas contain two lithium ions, a high capacity can be expected in theory (see Patent Documents 7 to 11 and Non-Patent Document 2). However, since the electron conductivity is extremely low, not only the conductive auxiliary agent is mixed in the electrode, but also carbon coating is attempted (see Non-Patent Documents 3 to 5).

Prior technical literature Patent literature

Patent Document 1 JP-A-2003-34534

Patent Document 2, JP-A-2006-302671

Patent Document 3, JP-A-2002-75364

Patent Document 4, JP-A-2003-272632

Patent Document 5, JP-A-2004-234977

Patent Document 6 JP-A-2003-59491

Patent Document 7 JP-A-2007-335325

Patent Document 8 Special Table 2005-519451

Patent Document 9 JP-A-2001-266882

Patent Document 10, JP-A-2010-108678

Patent Document 11 Japanese Patent Laid-Open Publication No. 2009-170401

Non-patent literature

Non-Patent Document 1 J. Moskon, R. Dominko, R. Cerc-Korosec, M. Gaberscek, J. Jamnik, J. Power Sources 174, (2007) 638-688.

Non-Patent Document 2 R. Dominko, M. Bele, M. Gaberscek, A. Meden, M. Remskar, J. Jamnik, Electrochem. Commun. 8, (2006) 217-222.

Non-Patent Document 3 Shao Bin, Taniguchi, 50th Battery Symposium Lecture Highlights, (2009) 111.

Non-Patent Document 4 Shao Bin, Taniguchi, and the 51st Battery Symposium Lecture Highlights, (2010) 211.

Non-Patent Document 5 Yi-Xiao Li, Zheng-Liang Gong, Yong Yang, J. Power Sources 174, (2007) 528-532.

Non-Patent Document 6 Kojima Koji, Kojima Minsho, Kosuke, Okumura Tomo, Kyuzen, The 51st Battery Symposium, (2010) 194.

Non-Patent Document 7 Uemura Yuichi, Kobayashi Ryoji, Doi Kyuyuki, Okada Satoshi, Yamaki Junichi, 50th Battery Symposium Lecture Highlights, (2009) 30.

As described above, lithium iron citrate (Li ₂ FeSiO ₄ ) or lithium manganese citrate (Li ₂ MnSiO ₄ ), and derivatives thereof whose elemental substitution or composition is changed as a basic structure can be expected to be theoretically Composition of high capacity (330mAh / g). In fact, there are few examples in which an available capacity (165 mAh/g) of 1 Li or more is obtained, and an effective capacity (247 mAh/g) of 1.5 Li has not been achieved, and Patent Document 7 has 60 to 130 mAh/ The capacity of g, Non-Patent Document 6 is an effective capacity of 190 mAh/g, and Non-Patent Document 7 has an effective capacity of 225 mAh/g.

However, actually, even if a high effective capacity is obtained and the internal resistance is high, since the high voltage as a battery is not obtained, the substantial energy density becomes low. Further, when the internal resistance is high, the heat generation of the battery becomes large, and the thermal design of the battery unit becomes difficult. Conventionally, since the theoretical capacity of lithium iron silicate or lithium manganese ruthenate is high and efforts have been made to increase the effective capacity, the inventors have pointed out that it is not sufficient to increase the effective capacity of light, and it is also necessary to reduce the internal resistance.

The present invention has been made in view of the above problems, and the present invention provides a positive electrode material for a lithium ion secondary battery which can obtain a low internal resistance, a positive electrode member for a lithium ion secondary battery using the same, and a lithium ion secondary battery. The positive electrode material for a lithium ion secondary battery is a positive electrode material for a lithium ion secondary battery containing an oxide having a theoretical capacity of 2 Li or more.

The present inventors have found that the oxide represented by the experimental formula Li ₂ MSiO ₄ represented by lithium iron ruthenate or lithium manganese ruthenate can reduce the internal resistance by making the ratio of lithium ions excessive.

That is, the present invention is based on the following:

(1) A positive electrode material for a lithium ion secondary battery comprising a positive electrode for a lithium ion secondary battery containing an oxide represented by an experimental formula: Li _2+x (M,M ^A )(Si,M ^B )O ₄ a material (wherein M is one or more elements selected from the group consisting of Fe, Mn, Co, and Ni, and M ^A and M ^B are substituted for one of M and Si, respectively, and compensates for x of Li ⁺ The element of charge, containing at least one of them, is characterized by 0<x≦0.25 in the experimental formula of the oxide.

(2) The positive electrode material for a lithium ion secondary battery according to (1), wherein the value of x is a multiple of 0.03125.

(3) The positive electrode material for a lithium ion secondary battery according to (1) or (2), wherein the M ^A is one or more elements selected from the group consisting of Li, Na, and K, and the M ^B is selected from the group consisting of B and Al. One or more elements of Ga, In, Sc, Y, Mg, Ca, Na, and K.

(4) The positive electrode material for a lithium ion secondary battery according to (1) or (2), wherein the oxide is an experimental formula of Li _{2+ x} Fe(Si, M ^B )O ₄ or Li _2+x Mn (Si) M ^B ) O ₄ indicates that M ^B is one or more elements selected from the group consisting of B, Al, and Ga.

(5) The positive electrode material for a lithium ion secondary battery according to (1) or (2), which is a composite of the foregoing oxide and a carbon material, wherein for the carbon material, the oxide of the composite is dispersed Island-like island structure, The average value of the equivalent circle diameter of the island island is 3 nm or more and 15 nm or less.

(6) The positive electrode material for a lithium ion secondary battery according to (5), wherein the composite system has particles having a size of from 1 μm to 20 μm, and voids are present inside the particles.

(7) The positive electrode material for a lithium ion secondary battery according to (6), wherein a void having a size smaller than the particle size of 200 nm or more is present inside the particle.

(8) The positive electrode material for a lithium ion secondary battery according to (7), wherein the void is present in an amount of 20% or more and 80% or less in accordance with an area ratio of the particle cross section.

(9) A positive electrode member for a lithium ion secondary battery, comprising a metal foil having a positive electrode layer comprising a positive electrode material for a lithium ion secondary battery of (1) or (2), and a binder .

(10) A lithium ion secondary battery comprising the positive electrode material for a lithium ion secondary battery according to (1) or (2) or the positive electrode member for a lithium ion secondary battery according to (9).

According to the present invention, it is possible to provide a positive electrode material for a lithium ion secondary battery which is excellent in internal resistance. Further, a positive electrode member for a lithium ion secondary battery having a low internal resistance and a lithium ion secondary battery can be obtained.

Used to implement the aspect of the invention

The cathode material for a lithium ion secondary battery of the present invention contains an oxide represented by the experimental formula Li _2+x (M,M ^A )(Si,M ^B )O ₄ (wherein M is selected from Fe One or more elements of the group consisting of Mn, Co, and Ni, and M ^A and M ^B are substituted for one of M and Si, respectively, and the element of charge for compensating for x of Li ⁺ contains at least one of a), in the experimental formula of the oxide, 0 < x ≦ 0.25.

That is, compared to the stoichiometric ratio in the general experimental formula Li ₂ MSiO ₄ such as lithium iron citrate, lithium manganese ruthenate, lithium cobalt ruthenate, lithium nickel ruthenate, etc., by setting a lithium in a specific range (more than 2 lithium), which can reduce internal resistance.

The oxide represented by the experimental formula Li ₂ MSiO ₄ represented by lithium iron citrate or lithium manganese citrate is such that lithium ions are doped between the sheets (layers) of the MSiO ₄ sheet (layer) and the same sheet (layer). In the structure, the MSiO ₄ flakes may have a apex of the oxygen tetrahedron of M and the oxygen tetrahedron of Si. Each of the sheets is considered to be negatively charged in a state in which lithium ions are doped, and electrostatic attraction is exhibited between the sheets through the lithium cations.

When lithium ions are delithized by charging, lithium ions existing between the sheets are lost, and the negative charge of each sheet is lost and is close to zero charge. As a result, the electrostatic attraction between the sheets is lost (or weakened), and misalignment easily occurs between the sheets. When the misalignment between the sheets is increased, the path of lithium ions moving between the sheets becomes complicated, and lithium ion migration becomes difficult, and internal resistance becomes high.

Further, in the case of such a layered structure, it is considered that the movement of electrons accompanying the insertion and removal of lithium ions is mainly limited to the inside of the sheet surface, and it is difficult for electrons to move between the sheets. However, in a structure in which lithium ions are more (excessly) mixed between the sheets, lithium which is inserted and removed by charge and discharge In addition to ions, the amount of lithium ions remaining between the sheets increases, and the sheets are fixed by electrostatic attraction, and the occurrence of misalignment between the sheets becomes difficult. That is, the diffusion path of lithium ions can be ensured, and the internal resistance can be lowered. Further, when lithium ions are excessively incorporated, they become a common surface, and the lithium ions or the oxygen-coordinated polyhedron of the lithium ions are transmitted to facilitate the movement of electrons between the sheets, thereby reducing the internal resistance.

Under this technical idea, it is found that when the excess amount x of lithium ions is 0 < x ≦ 0.25, the internal resistance can be lowered. Therefore, when x is 0 or less, the internal resistance cannot be lowered. Further, when x exceeds 0.25, lithium ions do not enter between the sheets, and as a result, even if it exceeds 0.25, the internal resistance is not further lowered.

The value of the excess amount x is preferably a multiple of 0.03125 within the above range. When it is the above multiple, a sublattice is formed and the structure is more stable. Therefore, it is difficult to cause a structural change even if the charge and discharge are repeated, and it becomes difficult to reduce the discharge capacity or increase the internal resistance.

The charge compensation to become an excess lithium ion is carried out by (i) substituting M ^A for M, (ii) substituting M ^B for Si, or combining both (i) and (ii).

In the case of M ^A , it is an element of 1 price. For example, Li, Na, K, etc. are mentioned. Particularly preferred is Li. For M ^B , it is an element of 3 price, 2 price, or 1 price. For example, B, Al, Ga, In, Sc, Y, Mg, Ca, Zn, Cu, Na, K, etc. are mentioned. The M ^A is one or more elements selected from the group consisting of Li, Na, and K, and the M ^B is selected from one or more elements selected from the group consisting of B, Al, Ga, In, Sc, Y, Mg, Ca, Na, and K. good.

The aforementioned charge compensation is further preferably carried out by (ii) the conducter. That is, Li _2+x Fe(Si,M ^B )O ₄ or Li _2+x Mn(Si,M ^B )O ₄ , and Si is substituted by M ^B . Further, in terms of effectively reducing the internal resistance, it is more preferable that M ^B is one or more of B, Al, and Ga.

Further, the present invention is a composite of the above-mentioned oxide and a carbon material, and as shown in Fig. 1, in the carbon material, the oxide is an island structure in which an island shape is dispersed, and the island of the island structure is converted into a circle. The average value of the diameter is preferably 3 nm or more and 15 nm or less.

The region of the oxide in the composite is plural, that is, because the carbon material in the composite is a matrix (continuous body), and the region of the oxide is dispersed (non-continuous), the lithium ion is accompanied by the aforementioned Since the electron mobility from the respective regions caused by the insertion and the detachment of each region can pass through the carbon material, all of the above regions act as active materials. Therefore, it is considered that a high effective capacity can be achieved. Further, when the size of the region is small, the distance in which the solid content of lithium ions diffuses becomes small, and the effective capacity tends to be high. In the case of the above oxide, since the conductivity is extremely small, a high effective capacity is obtained with an actual charge and discharge time, which is a crystal grain size which is required to be diffused in a solid of lithium ions in accordance with the charge and discharge time.

Specifically, when the circle-converted diameter of the area projected area of the oxide in the composite is 15 nm or less, a higher effective capacity can be obtained. When the diameter exceeds 15 nm, the lithium ion solid internal diffusion distance becomes large, and lithium ions cannot be diffused during the actual charge and discharge time. As a result, a high effective capacity cannot be obtained. On the other hand, the aforementioned lower diameter limit is the smallest size that easily retains lithium ions within the oxide structure. Therefore, when the diameter is less than 3 nm, it may be difficult to maintain lithium ions in the oxide structure.

The region of the oxide of the composite described above can be observed using a transmission electron microscope. The circle-converted diameter of the projected area is observed by a transmission electron microscope and can be calculated by image processing.

Specifically, in the binary transmission electron microscope image, the circle-converted diameter can be calculated by the average value of the diameters when the area of the circle is substituted. The circle-converted diameter is the average of the number of the aforementioned diameters of 20 or more. Usually, the average of 50 is used as the circle-converted diameter.

In the positive electrode material for a lithium ion secondary battery of the present invention, the content of the carbon material is preferably 2% by mass or more and 25% by mass or less.

When the content of the carbon material is less than 2% by mass, the electron conduction path to the current collector may not be sufficiently ensured, and excellent battery characteristics may not be obtained. On the other hand, when the content of the carbon material is more than 25% by mass, the ratio of the active material at the time of electrode formation is small, and there is a case where a high battery capacity cannot be obtained depending on the design or purpose of the battery design. Therefore, in the above range, excellent battery performance can be easily ensured, and it becomes possible to expand the range of selection of the battery design.

When the carbon material of the present invention contains elemental carbon, the content of the graphite skeleton carbon contained in the carbon material in the composite particles is preferably from 20 to 70%. When the content ratio of the graphite skeleton carbon is less than 20%, the electrical conductivity of the carbon material becomes low, and it becomes difficult to obtain a high capacity. On the other hand, when the content ratio of the graphite skeleton carbon exceeds 70%, the hydrophobic solution is hard to be impregnated, and it becomes difficult to obtain a high capacity.

The composite system has particles having a size of from 1 μm to 20 μm, and as shown in Fig. 1, it is preferred that a void exists in the interior of the particles.

In this way, high capacity and good coatability can be obtained without lowering the capacity. Since the particle size is large, it is easy to uniformly disperse the positive electrode material in the coating slurry, and since the fluidity of the slurry is also improved, coating unevenness is less likely to occur. Therefore, the shrinkage of the coating film which occurs during the coating process or the drying process is also uniformly generated, and the occurrence of cracks can also be suppressed. In particular, when the amount of coating is large, the aforementioned effects are remarkably exhibited. That is, when the size of the particles is less than 1 μm , the coatability may be deteriorated. On the other hand, when the size of the particles exceeds 20 μm , the unevenness of the surface of the coating film due to the particles may become uneven. The shape of the particles is particularly spherical.

Here, the size of the particles is a circle-converted diameter of a projected area of the particles which can be observed using a Transmission Electron Microscope (TEM) or a Scanning Electron Microscope (SEM). The circle-converted diameter is calculated by using a TEM image or an SEM image instead of the average of the diameters of the observed particles as a circular area. The circle-converted diameter is the average of the number of the aforementioned diameters of 20 or more. Usually, the average of 50 is used as the circle-converted diameter. The image of either TEM or SEM can achieve the above effects if it falls within the scope of the present invention.

It is preferable that the inside of the particle has a void having a size smaller than a particle diameter of 200 nm or more.

Due to the presence of the aforementioned voids in the interior of the particles, a high capacity can be obtained even at a high discharge rate. The reason for this is that since the electrolyte solution is impregnated in the aforementioned voids and can be kept in a sufficient amount, Li ⁺ ions in the interior of the particles and the electrolyte solution can be easily exchanged even at a high rate. On the other hand, in the case of no voids, since the electrolyte solution cannot penetrate a sufficient amount into the inside of the particles, Li ⁺ ions do not diffuse into the surface of the particles in the solid, and it becomes impossible to efficiently at a high rate. Inserted out of Li ⁺ ions. That is, there is a case where a high rate and a high capacity cannot be obtained.

The amount of the voids present is preferably 20% or more and 80% or less in accordance with the area ratio of the particle cross section. The reason for this is that the area ratio is set to 20% or more and 80% or less. When the ratio is less than 20%, a high discharge rate and a high capacity are not obtained. On the other hand, when the temperature exceeds 80%, a high discharge rate can be obtained. Capacity, but there is a case where the content of the active material in the electrode becomes difficult to increase.

The positive electrode material for a lithium ion secondary battery of the present invention can be used as a positive electrode layer containing at least a binder, which is used for forming a surface of a metal foil of a current collector, and can be used as a positive electrode member for a lithium ion secondary battery.

The aforementioned binder (also referred to as a binder or binder) plays the role of a binding active substance or a conductive additive.

The binder of the present invention is usually used in the production of a positive electrode of a lithium ion secondary battery. Further, in the case of the binder, it is preferred to chemically and electrochemically stabilize the electrolyte of the lithium ion secondary battery and the solvent thereof.

The binder may be either a thermoplastic resin or a thermosetting resin. For example, polyolefins such as polyethylene and polypropylene; polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoroethylene copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer may be mentioned. (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride- Fluorine-based resin such as hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer; styrene butadiene rubber (SBR); ethylene-acrylic acid copolymer or the Na ⁺ ion-crosslinked copolymer of product; ethylene - methacrylic acid copolymer or the Na ⁺ ion-crosslinked copolymer of the composition; an ethylene - methyl acrylate copolymer or a copolymer of the Na ⁺ ion crosslinked product; ethylene a methyl methacrylate copolymer or a Na ⁺ ion crosslinker of the copolymer; carboxymethyl cellulose or the like. In addition, these can also be used in combination. Among these materials, PVDF and PTFE are particularly preferred.

In general, the above-mentioned binder is used in a ratio of about 1 to 20% by mass based on the total amount of the positive electrode.

Further, the positive electrode layer of the positive electrode member for a lithium ion secondary battery may further contain a conductive auxiliary agent.

The conductive auxiliary agent is not particularly limited as long as it is a chemically stable electronic conductive material. For example, graphite such as natural graphite (flaky graphite) or artificial graphite; acetylene black; high surface superconducting carbon black (Ketjen Black); carbon black such as black, furnace black, lamp black, and hot carbon black; Other types: carbon materials such as carbon fibers, conductive fibers such as metal fibers; carbon fluoride; metal powders such as aluminum; zinc oxide; conductive whiskers such as potassium titanate; and conductivity of titanium oxide One type of these may be used alone or two or more types may be used in combination, such as a metal oxide or an organic conductive material such as a polyphenylene derivative. Among these, carbon materials such as acetylene black, high surface superconducting carbon black, and carbon black are particularly preferred.

Usually, the above-mentioned conductive auxiliary agent is used in a ratio of about 1 to 25% by mass based on the total amount of the positive electrode.

The positive electrode layer contains at least a positive electrode active material and a binder, and has a structure in which a gap in which an electrolyte solution can penetrate is formed. Further, the positive electrode layer may contain a conductive auxiliary agent in addition to the positive electrode active material and the binder.

As the metal foil-based conductive metal foil, for example, a foil made of aluminum or an aluminum alloy can be used. The thickness can be made from 5 μm to 50 μm .

A lithium ion secondary battery can be fabricated by using the above member for a lithium ion secondary battery. For example, in addition to the member for a lithium ion secondary battery, a lithium ion secondary battery may be configured as a negative electrode, a separator, and a nonaqueous electrolyte.

The negative electrode contains a binder (also referred to as a binder or binder) as needed for the negative electrode active material.

As the negative electrode active material relating to the negative electrode, those which can be doped and dedoped with lithium metal or Li ion can be used, and examples of the doping/dedoping Li ion include graphite and pyrolytic carbon. Carbon materials such as carbonaceous materials such as pyrocarbons, glassy carbons, organic polymer compounds, mesocarbon microspheres, carbon fibers, and activated carbon. In addition, an alloy such as Si, Sn, or In, or an oxide such as Si, Sn, or Ti which can be charged and discharged at a low potential close to Li, or a nitride such as Li and Co such as Li _2.6 Co _0.4 N can be used. The compound is used as a negative electrode active material. Further, it is also possible to replace one of the graphite with a metal or an oxide which is alloyed with Li.

In the case where graphite is used as the negative electrode active material, since the voltage at the time of full charge can be set to about 0.1 V on the basis of Li, it is possible to easily calculate the potential of the positive electrode by applying a voltage of 0.1 V to the battery voltage. It is preferable to easily control the charging potential of the positive electrode.

The negative electrode may have a structure in which a negative electrode layer containing a negative electrode active material and a binder is provided on the surface of the metal foil to be a current collector.

Examples of the metal foil include copper, nickel, titanium, or an alloy thereof, or a foil of stainless steel. As one of the preferable negative electrode current collector materials used in the present invention, copper or an alloy thereof can be exemplified. A preferred metal to be alloyed with copper is Zn, Ni, Sn, Al, or the like, and Fe, P, Pb, Mn, Ti, Cr, Si, As, or the like may be added in a small amount.

The separator may be any film having a large ion permeability and a predetermined mechanical strength and insulating properties. As the material, an olefin polymer, a fluorine polymer, a cellulose polymer, a polyimide, a nylon, a glass fiber, or an alumina fiber can be used. As the form, a non-woven fabric, a woven fabric, or a microporous film can be used.

In terms of material, it is preferably a mixture of polypropylene, polyethylene, polypropylene and polyethylene, a mixture of polypropylene and polytetrafluoroethylene (PTFE), and a mixture of polyethylene and polytetrafluoroethylene (PTFE). In particular, a microporous film is particularly preferred.

Further, a microporous film having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm is particularly preferred. The microporous film may be a single film or a composite film composed of two or more layers having different properties such as the shape, density, or the like of the micropores. For example, a composite film in which a polyethylene film and a polypropylene film are bonded together may be mentioned.

Generally, the nonaqueous electrolytic solution is composed of an electrolyte (supporting salt) and a nonaqueous solvent. The supporting salt in the lithium secondary battery mainly uses a lithium salt.

Examples of the lithium salt which can be used in the present invention include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiB ₁₀ Cl ₁₀ , and LiOSO ₂ C _n F _2n+1 . The fluorosulfonic acid (n is a positive integer of 6 or less) and the quinone imine salt represented by LiN(SO ₂ C _n F _2n+1 )(SO ₂ C _m F _2m+1 ) (m and n are respectively a positive metal of _{6 or less} ), a methyl metal salt represented by LiC(SO ₂ C _p F _2p+1 )(SO ₂ C _q F _2q+1 )(SO ₂ C _r F _2r+1 ) (p, q) And r may be a positive integer of 6 or less, a lithium salt of a lower aliphatic lithium carboxylate, LiAlCl ₄ , LiCl, LiBr, LiI, lithium chloroborate or lithium tetraphenylborate, or one of them may be used or Two or more kinds are used in combination. Among them, those in which LiBF ₄ and/or LiPF ₆ are dissolved are preferred.

The concentration of the supporting salt is not particularly limited, but the electrolyte per 1 liter is preferably 0.2 to 3 moles.

Examples of the nonaqueous solvent include propylene carbonate, ethyl carbonate, butyl carbonate, ethyl chloroacetate, trifluoromethyl ethyl carbonate, difluoromethyl ethyl carbonate, and carbonic acid. Monofluoromethylethyl ester, hexafluoromethyl acetate, trifluoromethyl acetate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, methyl formate , methyl acetate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl hydrazine, 1,3-dioxolane, 2,2-bis(trifluoromethyl)- 1,3-dioxolane, formamide, dimethylformamide, dioxolane, two Alkane, acetonitrile, nitromethane, diethoxyethane, phosphotriester, boric acid triester, trimethoxymethane, dioxolane derivative, cyclobutyl hydrazine, 3-methyl-2- Azolidinone, alkylsydnone (alkyl is propyl, isopropyl, butyl, etc.), propyl carbonate derivative, tetrahydrofuran derivative, diethyl ether, 1,3-propane sultone An aprotic organic solvent or an ionic liquid is used in combination of one or more of them.

Among these, a carbonate-based solvent, particularly preferably a cyclic carbonate and a non-cyclic carbonate are preferably used in combination. The cyclic carbonate is preferably ethyl carbonate or propylene carbonate. Further, the acyclic carbonate is preferably diethyl carbonate, dimethyl carbonate or ethyl methyl carbonate. Further, from the viewpoint of a high potential window or heat resistance, an ionic liquid is preferred.

Preferably, the electrolyte solution contains LiCF ₃ SO ₃ in an electrolyte solution in which ethylene carbonate, propyl carbonate, 1,2-dimethoxyethane, dimethyl carbonate or diethyl carbonate are appropriately mixed. An electrolyte solution of LiClO ₄ , LiBF ₄ and/or LiPF ₆ .

Particularly preferably, in a mixed solvent of at least one of propylene carbonate or ethyl carbonate and at least one of dimethyl carbonate or diethyl carbonate, selected from among LiCF ₃ SO ₃ , LiClO ₄ or LiBF ₄ At least one salt and an electrolyte of LiPF ₆ .

The amount of the electrolyte added to the battery is not particularly limited, but may be used depending on the amount of the positive electrode material or the negative electrode material or the size of the battery.

Further, in addition to the electrolyte solution, the following solid electrolyte can also be used. As a solid electrolyte, it is classified into an inorganic solid electrolyte and an organic solid electrolyte.

Examples of the inorganic solid electrolyte include a nitride of Li, a halide, an oxyacid salt, and the like. Among them, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, _x Li ₃ PO ₄ - _(1-x) Li ₄ SiO ₄ Li ₂ SiS ₃ , a phosphorus sulfide compound, and the like are effective.

In the case of an organic solid electrolyte, a polyoxyethylene derivative or a polymer comprising the derivative, a polyoxypropylene derivative or a derivative thereof The polymer, the polymer containing the ionic dissociation group, the mixture of the ionic dissociation group-containing polymer and the aprotic electrolyte, the phosphate polymer, and the polymer matrix material containing the aprotic polar solvent are effective. Further, there is also a method of adding polyacrylonitrile to an electrolytic solution. Further, a method of using an inorganic or organic solid electrolyte in combination is also known.

In addition, as the member for the lithium ion secondary battery, the lithium ion secondary battery can be used as the material for the lithium ion secondary battery. For example, a lithium ion secondary battery is formed by a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the positive electrode layer is formed of a material for a lithium ion secondary battery, a conductive auxiliary agent, and a binder. Made up.

The lithium ion secondary battery positive electrode material of the present invention can be produced by the following method as an example.

The oxide of the present invention can be produced by a method in which an oxide can be synthesized, such as a dry method or a wet method. For example, a solid phase method (solid phase reaction method), a hydrothermal method (hydrothermal synthesis method), a coprecipitation method, a sol ‧ gel method, and a gas phase synthesis method (physical vapor deposition method (Physical Vapor Deposition: PVD) Method), chemical vapor deposition (Chemical Vapor Deposition: CVD), spray pyrolysis, flame, calcination, and the like.

Hereinafter, an example produced by a solid phase method, a spray pyrolysis method, or a calcination method will be described.

The raw material used in the solid phase method contains a compound constituting the element of the above-mentioned oxide, and for example, an organic acid salt such as an oxide, a carbonate, an acetate or an oxalate is used. The compound was weighed and mixed with the composition ratio. As the mixing system, a wet mixing method, a dry mixing method, or the like can be used. and Further, the obtained mixture was fired to synthesize the above oxide. The oxide powder obtained by firing is pulverized as needed. In the case where the unreacted material remains, it is pulverized and then fired.

As a specific example, in the case of Li _2.0625 Mn(Si _0.9375 Al _0.0625 )O ₄ , for example, manganese dioxide, lithium carbonate, cerium oxide, or aluminum oxide may be weighed to form the chemical composition, and then mixed, and the mixed powder may be reduced. Manufactured in a gas atmosphere at a temperature of 700 to 900 ° C for 5 to 20 hours.

Further, in the case of Li _2.0625 Fe(Si _0.9375 Al _0.0625 )O ₄ , for example, lithium carbonate, iron (II) oxalate dihydrate, cerium oxide, or aluminum oxide may be weighed to form the chemical composition, and the mixed powder may be mixed. It is produced by firing in a reducing gas atmosphere at a temperature of 700 to 900 ° C for 5 to 20 hours.

The raw material used in the spray pyrolysis method is a compound containing an element constituting a desired oxide, and a compound dissolved in water or an organic solvent is used. The solution obtained by dissolving the compound can be made into a droplet by an ultrasonic wave, a nozzle (a fluid nozzle, a two-fluid nozzle, a four-fluid nozzle, etc.), and then the droplet can be introduced into a heating furnace at a temperature of 400 to 1200 ° C. The foregoing oxide is produced by thermal decomposition. Further heat treatment or pulverization as needed. Further, by including an organic compound in the raw material solution, an oxide containing a carbon material can be produced.

As a specific example, in the case of Li _2.03125 Mn(Si _0.96875 Al _0.03125 )O ₄ , for example, lithium nitrate, manganese (II) nitrate hexahydrate, colloidal vermiculite, and aluminum nitrate can be weighed into the above chemical composition and dissolved in water. . In addition, an organic compound may be further added to the solution, and examples of the organic compound include ascorbic acid, monosaccharide (glucose, fructose, galactose, etc.), disaccharide (sucrose, maltose, lactose, etc.), and polysaccharide (amylose, Cellulose, dextrin, etc.), polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyvinyl butyral, polyvinyl pyrrolidone, phenol, hydroquinone, catechol, maleic acid, citric acid, malonic acid , ethylene glycol, triethylene glycol, diethylene glycol butyl methyl ether, triethylene glycol butyl methyl ether, tetraethylene glycol dimethyl ether, tripropylene glycol dimethyl ether, glycerin, and the like. Further, for example, an ultrasonic atomizer can be used to form a solution in which a solution of the above-mentioned compound is dissolved, and nitrogen is introduced into a heating furnace at a temperature of 500 to 1000 ° C as a carrier gas, and is thermally decomposed.

Further, in the case of Li _2.03125 Fe(Si _0.96875 Al _0.03125 )O ₄ , for example, lithium nitrate, iron (III) nitrate nonahydrate, tetraethoxy decane, or secondary-butadiene alumina can be weighed to form the aforementioned chemical composition. Dissolved in water afterwards. Among them, tetraethoxy decane and secondary-butadiene alumina were previously dissolved in methoxyethanol, and the solution was dissolved in water. For example, the solution in which the above-mentioned compound is dissolved can be made into a droplet by an ultrasonic atomizer, and nitrogen can be introduced into a heating furnace at a temperature of 500 to 1000 ° C as a carrier gas, and thermally decomposed.

Next, an example of a production method using a baking method will be described.

The raw material used in the calcination method contains a compound constituting an element of a desired oxide, and a compound dissolved in water is used. In the case of an oxide containing an iron element, it is preferred to use an aqueous solution obtained by dissolving a steel pickling waste liquid or a rolled roll in hydrochloric acid to prepare the raw material. The above oxide can be produced by thermally decomposing an aqueous solution in which the above compound is dissolved into a calciner of a Ruthner type, a Lurigi type or a Chemirite type. Further heat treatment or pulverization as needed. Further, by including an organic compound in the raw material solution, an oxide containing a carbon material can be produced.

As a specific example, in the case of Li _2.0625 Mn(Si _0.9375 Al _0.0625 )O ₄ , for example, lithium acetate, manganese nitrate (II) hexahydrate, colloidal vermiculite, aluminum nitrate can be weighed to become the aforementioned chemical composition and dissolved in water. . The solution may be further dissolved in an aqueous solution in which the compound is dissolved, and the solution may be introduced into, for example, a Chemirite type calciner to be thermally decomposed at a temperature of 500 to 1000 °C. The pulverized particles obtained by wet pulverization by a bead mill may be further subjected to heat treatment in an inert gas atmosphere.

Further, in the case of Li _2.0625 Fe(Si _0.9375 Al _0.0625 )O ₄ , for example, lithium carbonate, colloidal vermiculite, aluminum (III) chloride hexahydrate is dissolved in a steel pickling waste liquid (for example, 3.0 mol (Fe)/L. In the hydrochloric acid waste liquid of the concentration, the concentration of the chemical composition ratio is prepared. Among them, 18% hydrochloric acid was added in advance to the steel pickling waste liquid in an appropriate amount to dissolve all the lithium carbonate. The solution can be further dissolved in an aqueous solution in which the compound is dissolved, and the solution can be introduced into, for example, a Ruthner-type calciner to be thermally decomposed at a temperature of 500 to 1000 °C. The pulverized particles obtained by wet pulverization by a bead mill may be further subjected to heat treatment in an inert gas atmosphere.

Examples of the organic compound to be a carbon source include ascorbic acid, monosaccharide (glucose, fructose, galactose, etc.), disaccharide (sucrose, maltose, lactose, etc.), and polysaccharide (amylose, cellulose, dextrin). Etc.), polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyvinyl butyral, polyvinylpyrrolidone, phenol, hydroquinone, catechol, maleic acid, citric acid, malonic acid, ethylene glycol, Triethylene glycol, diethylene glycol butyl methyl ether, triethylene glycol butyl methyl ether, tetraethylene glycol dimethyl ether, tripropylene glycol dimethyl ether, glycerin, and the like.

Examples of the compound containing an element constituting the above metal oxide include a metal, a hydroxide, a nitrate, a chloride, an organic acid salt, an oxide, a carbonate, a metal alkoxide, and the like.

Example (Example 1)

Use lithium nitrate (LiNO ₃ ), iron (III) nitrate nonahydrate (Fe(NO ₃ ) ₃ ‧9H ₂ O), tetraethoxy decane (hereinafter referred to as TEOS), secondary-butadiene alumina, magnesium nitrate Hexahydrate (Mg(NO ₃ ) ₂ ‧6H ₂ O), boric acid (H ₃ BO ₃ ), gallium nitrate (Ga(NO ₃ ) ₃ ‧nH ₂ O), Yttrium Isopropoxide, sodium nitrate (NaNO ₃ ) was used as a starting material. The above raw materials were dissolved in water to prepare an aqueous solution to have the respective composition ratios of Table 1-1.

Among them, TEOS was previously dissolved in methoxyethanol, and the solution was dissolved in water. In addition, in the case of using secondary-butadiene alumina or isopropoxide, the chemically modified with ethyl acetate is added to the methoxyethanol in which TEOS is dissolved and dissolved, and the solution is dissolved in water. . Further, glucose is added to the aqueous solution as an organic compound to be a carbon material. Except for sample No. 1-20, No. 1-21, and No. 1-26, the aqueous solution was sprayed and thermally decomposed by using a carrier gas containing nitrogen gas in a heating furnace heated to 800 ° C, respectively. Make a sample. Further, Sample No. 1-20 was sprayed into a heating furnace at 500 ° C, and Sample No. 1-21 was sprayed into a heating furnace at 400 ° C.

Sample Nos. 1-1 to No. 1-17 were further wet-pulverized, and then heat-treated at 500 ° C for 10 hours in 1% H ₂ /Ar. After the sample No. 1-18 was wet-pulverized, the above heat treatment was performed at 600 ° C for 3 hours at 1% H ₂ /Ar. After the sample No. 1-19 was wet-pulverized, the above heat treatment was performed at 800 ° C for 5 hours in 1% H ₂ /Ar. Sample No. 1-20 to No. 1-25 were neither subjected to the above pulverization nor heat treatment. Sample No. 1-26 was obtained by pulverizing the sample No. 1-22 and granulating it.

Further, the concentration of the metal ions in the preparation solution is a solution in the range of 0.1 to 0.35 mol/L in terms of oxide composition. The glucose is added in a range of 2 to 2.4 molar ratio of glucose to oxide. Further, the unpulverized sample is a spherical particle, and the size of the spherical particle is controlled by the metal ion concentration and the glucose content in the droplet.

The metal ion concentration and the glucose addition amount in the solution of each sample are shown in Table 1-1.

<Analysis of each sample>

The above analysis was carried out for each of the obtained samples as described above.

The phase confirmation was carried out using a powder X-ray diffraction apparatus (Ultima II manufactured by Rigaku). Since Sample Nos. 1-1 to No. 1-19 were heat-treated, there was a diffraction pattern similar to that of Li ₂ FeSiO ₄ . However, a sample with excess Li or element substitution was observed to be offset at the diffraction peak. Sample No. 1-20, No. 1-22 to No. 1-26 did not show a diffraction peak at 2θ=15 to 18° by the CuKα line, and a diffraction peak of a broad peak appeared at 2θ=33±2°. Crystallized. Sample No. 1-21. There was no amorphous of the diffraction peak at all.

The sample No. 1-1 to the sample No. 1-26 were observed using a transmission electron microscope (H-9000UHR III manufactured by Hitachi Ltd.). These samples were all composites of sea-island structures, and the circle-converted diameter of the island (oxide) was calculated by the above method, and the obtained circle-converted diameter of each sample is shown in Table 1-2.

Using a scanning electron microscope (JSM-7000F manufactured by JEOL Ltd.), the particles of sample No. 1-20 to No. 26 were observed, and the circle-converted diameter was calculated from the image as the size of the spherical particles. The values are shown in the "particle size" column in Table 1-2. In addition, since samples No. 1-1 to No. 1-19 were pulverized to a size of 0.1 μm, non-particles were used, and fine particles having different shapes and sizes were used. Further, in the sample No. 1-26, the sample No. 1-22 was pulverized and granulated, and the granules were granulated into spherical particles. Furthermore, the particles can also be observed by a transmission electron microscope, and the size of the particles can also be obtained by a transmission electron microscope.

Further, the sections of the sample No. 1-20 to No. 26 of the particles were also observed by a scanning electron microscope. A void of 200 nm or more in the particle was selected from the image, and the area ratio was determined as the amount of the void. Sample No. 1-20 to No. 25 are values as shown in the "area ratio" column of "the void in the particle" shown in Table 1-2. In the sample No. 1-26, the particles of the sample No. 1-22 were pulverized and granulated, and the particles were dense inside, and there was no large gap of 200 nm.

The content of the carbon material contained in each sample was measured using a carbon-sulfur analyzer EMIA-320V manufactured by Horiba, Ltd., and is shown in Table 1-2.

<Evaluation of battery characteristics>

The battery characteristics evaluation of each sample was carried out as follows.

First, each sample was mixed with acetylene black powder and polytetrafluoroethylene powder in a weight ratio of 70:25:5 by a mortar, and then pressed onto a titanium mesh to prepare a positive electrode.

A metal lithium foil was used for the negative electrode, and a nickel foil having a thickness of 20 μm was used for the negative electrode current collector.

Further, as the electrolytic solution, a nonaqueous electrolytic solution obtained by dissolving 1.0 mol/L of LiPF ₆ in a mixed solvent of a molar ratio of ethyl carbonate to dimethyl carbonate of 1:2 was used, and the separator was used in a thickness of 25 μm. The porous polypropylene is equipped with a CR2032 coin battery in an argon glove box.

Each of the samples was prepared into five coin-type batteries, and each of them was subjected to a charge and discharge test in a 25 ° C thermostatic chamber to measure the initial discharge capacity. First, the initial charge and discharge test was carried out by repeating four times of pre-charge and discharge in a voltage range of 1.5 to 5.0 V and a C-CV condition of 0.1 C, and then charging 1.5 Li under a CC-CV condition of 0.1 C, and measuring the discharge capacity as a result. Initial charge and discharge capacity. In the column of “Initial Charge and Discharge Capacity” in Table 1-2, the initial charge and discharge capacity of each of the three coin-type batteries for each sample is measured, and the initial charge and discharge capacities of the three coin-type batteries whose maximum and minimum values are excluded are described. The average value.

The effect of reducing the internal resistance was determined from the discharge curve of the initial discharge capacity obtained at a voltage of 100 mAh/g, and the voltage was increased to determine that the internal resistance was lowered. Regarding this voltage, the discharge curve of each of the samples was determined from the discharge curve of the five-coin type battery, and the average value of the voltages of the three coin-type batteries excluding the maximum value and the minimum value is shown in Table 1-2.

Further, the charge and discharge were repeated until the 20th cycle, and the slope of the voltage change of 100 mAh/g from the discharge curve of 20 cycles to 25 cycles (voltage change per cycle) was obtained as the effect of reducing the internal resistance. The stability of each sample is shown in Table 1-2.

In Table 1-1 and Table 1-2, the sample No. 1 in which the value of x exceeds 0 is compared with the voltage of 100 mAh/g of sample No. 1-1 and No. 1-3 of which the value of x is 0. 2. No.1-4~No.1-11, No.1-13~1-20, No.1-22~No.1-26, the voltage became high, and the internal resistance reduction effect was observed. In sample No. 1-12, since the value of x exceeded 0.25, the effect of reducing the internal resistance was not observed. Sample No. 1-21 did not form a sufficient oxide, and almost no charge and discharge occurred.

Further, for the case where the value of x is a multiple of 0.03125 and the case of a multiple of 0.03125, the result of the charge compensation by Al is shown in Table 1-1 and Table 1-2, and when the value of x is a multiple of 0.03125. It is excellent in the stability of the internal resistance reduction effect. Even if the element of charge compensation is an element other than Al, the same tendency can be obtained.

Furthermore, the evaluation of the coating property was performed by the sample No. 1-20 - No. 1-26. Each of 90% by mass of each sample was mixed with 4% by mass of polyvinylidene fluoride (PolyVinylidene DiFluoride, PVDF) and 6% by mass of acetylene black in a dispersion solvent (N-methylpyrrolidone, NMP) to prepare a slurry. The slurry was applied to an aluminum foil having a thickness of 20 μm using a BAKER-type applicator having a gap of 300 μm , and dried in a dryer at 100 °C. The surface of the coating film after drying was visually observed, and the unevenness of the surface or the occurrence of cracks was evaluated as "poor coating property", the surface was flat, and no crack was observed, and the coating property was evaluated as "good coating property".

Sample No. 1-20 to No. 1-22 and No. 1-24 to No. 1-26 are results of "good coatability". Since sample No. 1-23 was a secondary fine particle, it was a result of "poor coating property".

Furthermore, those having a moderate void in the particles exhibit excellent discharge capacity even at a high rate.

(Example 2)

As a starting material, lithium nitrate (LiNO ₃ ), manganese (II) nitrate hexahydrate (Mn(NO ₃ ) ₂ ‧6H ₂ O), colloidal vermiculite, aluminum nitrate nonahydrate (Al(NO ₃ ) ₃ ) was used. ‧9H ₂ O), magnesium nitrate hexahydrate (Mg(NO ₃ ) ₂ ‧6H ₂ O), boric acid (H ₃ BO ₃ ), gallium nitrate (Ga(NO ₃ ) ₃ ‧nH ₂ O), niobium nitrate Hydrate (Y(NO ₃ ) ₃ ‧6H ₂ O), sodium nitrate (NaNO ₃ ). The above raw materials were dissolved in water to prepare an aqueous solution, and the composition ratios of Table 2-1 were obtained. Further, glucose is added to the aqueous solution as an organic compound to be a carbon material. Except for sample No. 2-21, a sample was prepared by spray-thermal decomposition of the aqueous solution using a carrier gas containing nitrogen gas in a heating furnace heated to 600 °C.

Sample Nos. 2-1 to No. 2-17 were further wet-pulverized, and then heat-treated at 700 ° C for 5 hours in 1% H ₂ /Ar. After the sample No. 2-18 was wet-pulverized, the above heat treatment was performed at 800 ° C for 5 hours in 1% H ₂ /Ar. After the sample No. 2-19 was wet-pulverized, the above heat treatment was performed at 950 ° C for 3 hours in 1% H ₂ /Ar. Sample No. 2-20 was neither subjected to the above pulverization nor heat treatment. Sample No. 2-21 was obtained by pulverizing sample No. 2-20 and granulating.

Further, the concentration of the metal ions in the preparation solution was a solution in which the oxide composition was 0.35 mol/L. The glucose is added in a molar ratio of glucose to oxide. Further, the unpulverized sample was a spherical particle.

<Analysis of each sample>

The same analysis as in Example 1 was carried out for each of the obtained samples No. 2-1 to No. 2-21.

In the case of X-ray diffraction samples No. 2-1 to No. 2-21, since samples No. 2-1 to No. 2-19 were heat-treated, they were similar to Li ₂ MnSiO ₄ crystals. Diffraction pattern. However, a sample with excess Li or element substitution was observed to be offset at the diffraction peak. Sample Nos. 2-20 and No. 2-21 used a CuKα line to exhibit a diffraction peak at 2θ=15 to 18°, and a crystal of a broad peak diffraction peak appeared at 2θ=33±2°.

Through the TEM observation, the samples No. 2-1 to No. 2-21 were all complexes of the island structure, and the circle-converted diameter of the island (oxide) was calculated by the above method, and the obtained circle of each sample was converted into a circle. And is shown in Table 2-2.

The spherical particles of sample No. 2-20 to No. 2-21 were observed by SEM, and the circle-converted diameter was calculated from the image as the size of the spherical particles. The values are shown in the "Particle Size" column of Table 2-2. In addition, Sample No. 2-1 to No. 2-19 are non-spherical particles which are pulverized to a size of 0.1 μm, and are fine particles having different shapes and sizes. Further, in the sample No. 2-21, the sample No. 2-20 was pulverized and granulated, and the granules were granulated into spherical particles.

Further, the cross sections of the sample No. 2-20 to No. 2-21 of the particles were also observed by SEM. A void of 200 nm or more in the particle was selected from the image, and the area ratio was determined as the amount of the void. Sample No. 2-20 is a value as shown in the "area ratio" column of "the void in the particle" shown in Table 2-2. In the sample No. 2-21, the particles of the sample No. 2-20 were pulverized and granulated, and the inside of the particles was dense, and there was no large gap of a size of 200 nm.

<Evaluation of battery characteristics>

Regarding the evaluation of the battery characteristics, only the following points are different from those of the first embodiment.

First, the initial charge and discharge test was carried out by repeating the preliminary charge and discharge with a voltage range of 1.0 to 5.0 V and a C-CV condition of 0.1 C, and then charging 250 mAh/g under a CC-CV condition of 0.1 C, and measuring the discharge capacity. As the initial charge and discharge capacity.

The internal resistance reduction effect was obtained by determining the discharge curve of the initial discharge capacity at a voltage of 140 mAh/g, and the voltage was increased to determine that the internal resistance was lowered. Further, the charge and discharge were repeated until 10 cycles, and the slope of the voltage change of 140 mAh/g from the discharge curve from 5 cycles to 10 cycles (voltage change per cycle) was obtained as the effect of reducing the internal resistance. Stability.

In Table 2-1 and Table 2-2, the sample No. 2 in which the value of x exceeds 0 is compared with the voltage of 140 mAh/g of sample No. 2-1 and No. 2-2 with an x value of 0. 3~No.2-8, No.2-10~No.2-21, the voltage became high, and the internal resistance reduction effect was observed. In sample No. 2-9, since the value of x exceeded 0.25, the effect of reducing the internal resistance was not observed.

Further, for the case where the value of x is a multiple of 0.03125 and the case of a multiple of 0.03125, the result of the charge compensation by Al is shown in Table 2-1 and Table 2-2, and when the value of x is a multiple of 0.03125. It is excellent in the stability of the internal resistance reduction effect. Even if the element of charge compensation is an element other than Al, the same tendency can be obtained.

In addition, the evaluation of the coating property was performed by the sample No. 2-20 - No. 2-21, and it was the result of "good coatability." Furthermore, those having a moderate void in the particles exhibit excellent discharge capacity even at a high rate.

(Example 3)

As a starting material, lithium carbonate (Li ₂ CO ₃ ), magnesium carbonate (MgCO ₃ ), cobalt oxide (CoO), cerium oxide (SiO ₂ ), boric acid (H ₃ BO ₃ ), γ-alumina (Al) are used. ₂ O ₃ ), gallium oxide (Ga ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ), sodium carbonate (Na ₂ CO ₃ ), and each oxide powder described in the composition column of Table 3 was prepared by a solid phase reaction method. .

First, each of the above raw materials was weighed and combined in the same manner as in the composition column of the composition column shown in Table 3, and wet-mixed for 12 hours in a ball mill using methanol. However, in the case of using boric acid, dry mixing is carried out. Each of the obtained mixtures was fired at 800 ° C for 24 hours in a nitrogen atmosphere, followed by pulverization by a planetary ball mill. Further, the pulverized powder was fired at 950 ° C for 12 hours in a nitrogen atmosphere to prepare an oxide powder of Table 3.

Each of the oxide powders prepared as described above was previously mixed with 10% by mass of acetylene black. The mixing method of acetylene black was carried out by wet mixing each oxide powder with acetylene black in a ball mill using methanol for 12 hours. The resulting mixture was fired at 400 ° C for 5 hours under a nitrogen atmosphere.

<Analysis of each sample>

The same analysis as in Example 1 was carried out for each of the obtained samples No. 3-1 to No. 3-17.

In the case of X-ray diffraction samples No. 3-1 to No. 3-17, samples No. 3-1 to No. 3-17 of Table 3 are similar to those of Li ₂ CoSiO ₄ crystal. The picture is taken as the main phase. However, a sample with excess Li or element substitution was observed to be offset at the diffraction peak.

<Evaluation of battery characteristics>

Regarding the evaluation of the battery characteristics, only the following points are different from those of the first embodiment.

First, the initial charge and discharge test was carried out by repeating four times of pre-charge and discharge in a voltage range of 1.0 to 5.0 V and a C-CV condition of 0.1 C, and then charging 200 mAh/g under a CC-CV condition of 0.1 C to measure the discharge capacity. As the initial charge and discharge capacity.

For the internal resistance reduction effect, the discharge curve of the initial discharge capacity was determined to obtain a voltage of 100 mAh/g, and the voltage was increased to determine that the internal resistance was lowered. Further, the charge and discharge were repeated until the 20th cycle, and the slope of the voltage change of 100 mAh/g from the discharge curve of 15 cycles to 20 cycles (voltage change per cycle) was obtained as the effect of reducing the internal resistance. Stability.

In Table 3, samples No. 3-3 to No. 3-8 in which the value of x exceeds 0 compared with the voltage of 100 mAh/g of samples No. 3-1 and No. 3-2 having an x value of 0. In No. 3-10 to No. 3-17, the voltage became high, and an internal resistance reduction effect was observed. Sample No. 3-9 had an effect of reducing the internal resistance when the value of x exceeded 0.25.

Further, for the case where the value of x is a multiple of 0.03125 and the case of a multiple of 0.03125, the result of the charge compensation by Al is shown in Table 3. When the value of x is a multiple of 0.03125, the internal resistance is lowered. The stability of the effect is excellent. Even if the element of charge compensation is an element other than Al, the same tendency can be obtained.

In addition, iron (II) oxalate dihydrate (FeC ₂ O ₄ ‧2H ₂ O), manganese carbonate (MnCO ₃ ), or nickel oxide (NiO) is used as a starting material, and the same solid phase reaction method as described above is also used. Making Li _2+x (Fe _1-y M ^A _y )(Si _1-z M ^B _z )O ₄ , Li _2+x (Mn _1-y M ^A _y )(Si _1-z M ^B _z )O ₄ ^A sample of Li _2+x (Ni _1-y M ^A _y )(Si _1-z M ^B _z )O ₄ was confirmed to have the same effect.

Fig. 1 is a schematic view showing the internal structure of the composite of the present invention and a TEM image of the fracture portion.

Claims (10)

A positive electrode material for a lithium ion secondary battery, which is a positive electrode material for a lithium ion secondary battery containing an oxide represented by an experimental formula: Li _2+x (M,M ^A )(Si,M ^B )O ₄ (wherein M is one or more elements selected from the group consisting of Fe, Mn, Co, and Ni; and M ^A and M ^B are substituted for one of M and Si, respectively, to compensate for the charge of x of Li ⁺ The element, which contains at least one of them, is characterized by 0<x≦0.25 in the experimental formula of the oxide. The positive electrode material for a lithium ion secondary battery according to claim 1, wherein the value of x is a multiple of 0.03125. The positive electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the M ^A is one or more elements selected from the group consisting of Li, Na, and K, and the M ^B is selected from the group consisting of B, Al, Ga, and One or more elements of Sc, Y, Mg, Ca, Na, and K. The cathode material for a lithium ion secondary battery according to claim 1 or 2, wherein the oxide is experimentally Li _2+x Fe(Si,M ^B )O ₄ or Li _2+x Mn(Si,M ^B )O _{In the case of 4} , M ^B is one or more elements selected from the group consisting of B, Al, and Ga. The cathode material for a lithium ion secondary battery according to claim 1 or 2, which is a composite of the oxide and the carbon material, wherein for the carbon material, the oxide of the composite exhibits an island structure dispersed in an island shape The average value of the circle-converted diameter of the island island is 3 nm or more and 15 nm or less. The positive electrode material for a lithium ion secondary battery according to claim 5, wherein the composite system has particles having a size of 1 μm or more and 20 μm or less, and voids are present inside the particles. The positive electrode material for a lithium ion secondary battery according to claim 6, wherein a void having a size smaller than the particle size of 200 nm or more is present inside the particle. The positive electrode material for a lithium ion secondary battery according to claim 7, wherein the void is present in an amount of 20% or more and 80% or less in accordance with an area ratio of the particle cross section. A positive electrode member for a lithium ion secondary battery, comprising a metal foil having a positive electrode layer comprising a positive electrode material for a lithium ion secondary battery according to claim 1 or 2, and a binder. A lithium ion secondary battery using the positive electrode material for a lithium ion secondary battery according to claim 1 or 2 or the positive electrode member for a lithium ion secondary battery according to claim 9.